Relationships of plant species richness, grazing, and aridity with soil
organic carbon in Xinjiang (China) grassland
Abstract
Soil carbon is a critical ecosystem function in drylands. In these
ecosystems, positive relationships between plant species richness (SR)
and soil carbon storage (SOC) that have been found in biodiversity
experiments and observational studies may be reduced by grazing and
aridity. However, studies about the extent to which SR, grazing
intensity, and aridity are interactively and directly or indirectly
related with SOC so far provided mixed results. Using a network of 199
grassland sites across a large aridity gradient in western China,
selected to represent low, medium, and high grazing intensity, we found
that SOC at the depth of 0–30 cm was positively related with SR and, to
a lesser degree, with grazing intensity. Aridity had no direct
relationship with SOC but affected it indirectly and negatively via its
negative relationships with both SR and grazing intensity and via its
positive relationship with soil pH. There were no indications that
grazing intensity could modify the positive SR–SOC relationship,
possibly because very high grazing intensities did not occur in the
study region. We conclude that current levels of SR and grazing
intensity should be maintained to avoid SOC-loss and CO2 release form
grassland under predicted aridity increases in the study region.